The present invention involves a low current impulse generating circuit suitable for use in cardiac pacers.
Conventional cardiac pacers or pacemakers utilize suitable low power drain circuits to generate the impulses used for heart stimulation. While additional circuits and circuit components are also provided, one fundamental pulse generating circuit comprises a complementary astable multivibrator, such as disclosed in U.S. Pat. No. 3,717,512, wherein two transistors of opposite conductivity type are connected across a power source and to each other by a plurality of resistors and a condenser. In order to achieve a sufficient stimulation voltage in pacemakers of this type and in view of the undesirable voltage instability of such prior art circuits at low operating potentials, it has generally been necessary to utilize a plurality of cells as the power source with the attendant problems presented thereby. It is accordingly desirable to minimize the voltage instability and power drain of such multivibrator circuits so that long pacemaker life may be achieved while using only a single cell as a power source. The present invention is directed to providing such a multivibrator circuit along with additional circuitry resulting in a highly reliable, low voltage, low power drain, supply voltage insensitive, stable pulse generator.